World demand for refined fossil fuels is ever-increasing and will eventually outstrip the supply of high quality crude oil. As the shortage of high quality crude oil increases there will be an increasing demand to find ways to process lower quality feedstocks and extract value added fuel components from them. Lower quality feedstocks contain relatively high quantities of hydrocarbons that have a boiling point of 524° C. or higher. They also contain relatively high concentrations of sulfur, nitrogen and/or metals. High boiling fractions typically have a high molecular weight and/or low hydrogen/carbon ratio like asphaltenes, Such compounds present in heavy oils are difficult to process and commonly cause coking and fouling of fixed bed hydroprocessing catalysts systems and hydroprocessing equipment. The coking and fouling reactions involved in hydroprocessing of heavy oil are undesirable as it greatly increases the catalyst and maintenance costs of processing heavy oils.
Converting heavy oil fractions into useful end products requires extensive processing, including reducing the boiling point of the heavy oil, increasing the hydrogen-to-carbon ratio and removing impurities such as metals, sulfur, nitrogen and carbon forming compounds. As the existing commercial catalytic hydrocracking processes, when used with heavy oil, rapidly undergo catalyst deactivation, new process technologies which enable to handle heavy oils more effectively are needed.
One promising technology for hydroprocessing heavy oils uses a hydrocarbon-soluble molybdenum salt that decomposes in the heavy oil during hydroprocessing to form, in situ, molybdenum sulfide, which can act as a hydroprocessing catalyst. The performance of oil soluble molybdenum catalysts depends significantly on the concentration of the catalyst in the heavy oil and on how well the catalyst precursor can be dispersed in the heavy oil. Improvements that can increase the percent of metal in the catalyst precursor while maintaining or improving solubility can improve the efficiency of hydrocracking heavy oils using oil soluble molybdenum compounds. Further, the degree of dispersion of the catalyst also strongly affects its performance. Although high levels of catalyst dispersion can be achieved by adopting efficient process conditions, addition of oil-soluble catalyst precursors seems the best way to promote a good dispersion of the catalyst species in the complex hydrocarbon matrix.
A significant problem with commercializing oil soluble molybdenum catalysts is the cost of the catalyst which leads to difficulty in terms of the economic viability of the overall process. However, even small improvements in catalyst performance can increase in output of fuels and other useful products and/or the reduced use of the catalyst and thus have a significant benefit to the overall cost of the hydrocracking process.
A number of oil-soluble metal catalyst used in hydroconversion process and their method of preparation are reported in various patents. Relevant patents related to the present invention are provided below:
One such process is disclosed in U.S. Pat. No. 5,578,197 to Cyr et al., in which the molybdenum sulfide catalyst, once formed in situ, is highly effective for breaking up of asphaltenes and thus preventing fouling and coking.
U.S. Pat. No. 8,445,399 B2 discloses a hydrocarbon soluble molybdenum catalyst precursor in a portion of the molybdenum atoms has an oxidation state of 3+ such that the average oxidation state is less than about 3.5+. Although such catalysts can form molybdenum sulfides for the hydroconversion of heavy oil feedstocks, the manufacture of precursor species requires complex procedures like treating with a reducing agent like hydrogen at high temperatures.
U.S. Pat. No. 7,842,635 reports a bimetallic catalyst system in which molybdenum along with another transition metal like Co, Ni or Fe is complexed with organic compounds like 2-ethyl hexanote to form an oil soluble catalyst system which is a mixture of complexes of molybdenum and the transition metal salt. However, since the Mo and transition metal complexes are prepared either sequentially at different temperatures or in separate vessels and then mixed, synergistic effects by their atomic dispersion has not been explored.
U.S. Pat. No. 3,161,585 discloses a hydro-refining process in which petroleum oil containing a colloidally dispersed catalyst selected from the group consisting of a metal of Groups VB and VIB, an oxide of said metal and a sulfide of said metal is reacted with hydrogen at hydro refining conditions. This patent teaches that the concentration of the dispersed catalyst, calculated as the elemental metal, in the oil is from about 0.1 weight percent to about 10 weight percent of the initial oil feedstock.
U.S. Pat. No. 3,331,769 discloses a hydrorefining process in which a metal component of Group VB, Group VIB or iron group metal colloidally dispersed in a hydrocarbonaceous oil is reacted in contact with a fixed bed of a conventional supported hydrodesulfurization catalyst in the hydrorefining zone. The concentration of the dispersed metal component which is used in the hydrorefining stage in combination with the supported catalyst ranges from 250 to 2,500 weight parts per million (wppm).
U.S. Pat. No. 3,657,111 discloses a process for hydrorefining asphaltene-containing hydrocarbon oil which comprises dissolving in the oil a hydrocarbon-soluble oxovanadate salt and forming a colloidally dispersed catalytic vanadium sulfide in situ within the oil and subsequently by reacting the resulting solution, at hydrorefining conditions, with hydrogen and hydrogen sulfide.
U.S. Pat. No. 4,066,530 discloses hydroconversion in the presence of an iron component and a catalytically active other metal component prepared by dissolving an oil-miscible metal compound in the oil and converting the metal compound in the oil to the corresponding catalytically active metal component.
In addition, oil-soluble metal compositions are also known for improving the properties of lubrication oils for internal combustion engines and in industrial lubricating applications. For example, U.S. Pat. Nos. 8,426,608 B2 and 8,476,460 disclose the preparation of molybdated succinimide complex. This invention disclosed that, in order to obtain lubrication oil that exhibits low friction and wear, the amine portion of the molecule is required to be pretreated with unsaturated carboxylic acids or carboxylic acid ester. The use of amide based molybdenum complex suitable for lubrication oil application was also reported by U.S. Pat. No. 8,183,189 in which the amide is derived from a carboxylic acid component and a polyamine component.